The number of reported cases of the water bug cryptosporidiosis has now reached more than 100.

The Northern Ireland Eastern Health Board confirmed on Thursday that 106 people had now been taken ill.

On Wednesday the Northern Ireland Water Service said it had identified the source of infection of the cryptosporidium bug which has caused widespread illness in Belfast.

The team investigating the outbreak believes it has traced its origins to the Dunore Point Water Treatment Plant on the eastern shore of Lough Neagh.

It is understood the contamination was caused by a blocked drain which allowed untreated water into the filtration system.

"I am absolutely convinced that the water supplied to the Belfast population now is absolutely safe.''

Dr Brian Morgan

The illness has an incubation period of a week to 10 days, so public health doctors are expecting further cases.

The cryptosporidium parasite can cause vomiting and chronic diarrhoea, and is particularly debilitating for the elderly, young children and the sick.

It can also prove fatal.

Health experts say cryptosporidiosis in immuno-compromised people often results in a chronic life threatening gastro-enteritis with a high mortality rate.

Special team

However, Dr Brian Morgan, the Eastern Board's consultant in communicable disease control, said he was satisfied that there was no further risk from drinking tap water.

Dr Brian Morgan: Water is `absolutely safe'

Speaking on Wednesday, he said: "I think this must be described as a very unusual set of circumstances, which in fact resulted in a combination of events - of themselves each unusual - which combined to cause a contamination which is extremely unusual.

"I am absolutely convinced that the water supplied to the Belfast population now is absolutely safe.''

The discovery follows an increase in the number of cases of the stomach bug in south and west Belfast.

Eighty-nine of the 106 cases have emerged since the end of February.

A special team has been set up at the Water Service's Communicable Disease Surveillance Centre to investigate the new outbreak.